CN108270451A - A kind of Enhancement Method of quasi- fluxoid LDPC code applied to quantum communication system - Google Patents

A kind of Enhancement Method of quasi- fluxoid LDPC code applied to quantum communication system Download PDF

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CN108270451A
CN108270451A CN201810057878.7A CN201810057878A CN108270451A CN 108270451 A CN108270451 A CN 108270451A CN 201810057878 A CN201810057878 A CN 201810057878A CN 108270451 A CN108270451 A CN 108270451A
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CN108270451B (en
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王云江
王治春
石莎
刘阳
王增斌
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Xidian University
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M13/00—Coding, decoding or code conversion, for error detection or error correction; Coding theory basic assumptions; Coding bounds; Error probability evaluation methods; Channel models; Simulation or testing of codes
    • H03M13/03—Error detection or forward error correction by redundancy in data representation, i.e. code words containing more digits than the source words
    • H03M13/05—Error detection or forward error correction by redundancy in data representation, i.e. code words containing more digits than the source words using block codes, i.e. a predetermined number of check bits joined to a predetermined number of information bits
    • H03M13/11—Error detection or forward error correction by redundancy in data representation, i.e. code words containing more digits than the source words using block codes, i.e. a predetermined number of check bits joined to a predetermined number of information bits using multiple parity bits
    • H03M13/1102—Codes on graphs and decoding on graphs, e.g. low-density parity check [LDPC] codes
    • H03M13/1148—Structural properties of the code parity-check or generator matrix
    • H03M13/116—Quasi-cyclic LDPC [QC-LDPC] codes, i.e. the parity-check matrix being composed of permutation or circulant sub-matrices

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Abstract

The invention belongs to Technique on Quantum Communication fields, disclose a kind of Enhancement Method of the quasi- fluxoid LDPC code applied to quantum communication system；It solves under long code application scenarios, the problem of quasi- fluxoid LDPC code error-correcting performance is bad；The realization step of the present invention：Based on European geometrical construction quasi-cyclic matrix HEG；To HEGIt processes to obtain the quasi-cyclic matrix H with even number submatrix；Quasi- fluxoid LDPC code is constructed based on H；Row LS-SVM sparseness is done to H, constructs enhanced quantized code；Using BP algorithm into row decoding.The present invention does row LS-SVM sparseness by being directed at the check matrix of internal circulating load subcode so that obtains better error-correcting performance in the case of similary code length.Its application scenarios is expanded into long code field.

Description

A kind of Enhancement Method of quasi- fluxoid LDPC code applied to quantum communication system
Technical field
The invention belongs to Technique on Quantum Communication fields more particularly to a kind of quasi- fluxoid low-density parity to examine LDPC The Enhancement Method of (low-density parity-check) code.
Background technology
Quantum communications and quantum calculation theory are that the communication system of structure efficiently, safe specifies direction.But due to moving back The presence of coherent phenomena causes quantum state to be easy to be destroyed, this becomes the problem that quantum communications must pull against.For this purpose, There has been proposed Quantum Error Correcting Codes theories.Wherein quantum low-density parity check LDPC code is the one kind limited very close to Hash capacity The error control coding haveing excellent performance can improve the reliability of quantum communication system.
At present, the prior art commonly used in the trade is：Utilize the verification of classical quasi-circulating low-density parity check LDPC code Matrix constructs easy characteristic the different and mutually orthogonal sparse matrix of two structures, and structure based on this with circular matrix Produce quasi- fluxoid low-density checksum LDPC code.The quantized code that this kind of code is largely solved on quaternary domain is deposited Many Fourth Rings the problem of.Therefore confidence spread BP (Belief Propagation) algorithms are utilized into error correction during row decoding It can get a promotion.But for the code of the type, with the increase of code length, code check is fast approached in one, is caused in long code application Since check bit number deficiency causes error-correcting performance power to be limited under scene.
In conclusion problem of the existing technology is：For existing quasi- fluxoid low-density checksum LDPC Code, once code length determines, code check can also determine therewith.Code check can be fast approached in 1 under long code application scenarios, this can cause Since check bit number deficiency causes error correcting capability to decline during decoding.So the quantized code of the type is only used for middle short code Scene.
Solve the difficulty and meaning of above-mentioned technical problem：In the construction rules without prejudice to quantized code, the present invention carries Go out a kind of Enhancement Method of quasi- fluxoid low-density checksum LDPC code, obtained by the number for increasing check bit better Error-correcting performance, by the application scenarios of the type code, therefrom short code scene expands to long code scene.
Invention content
In view of the problems of the existing technology, the present invention proposes a kind of quasi- fluxoid applied to quantum communication system The Enhancement Method of LDPC code.
The invention is realized in this way a kind of enhancing side of quasi- fluxoid LDPC code applied to quantum communication system Method, the Enhancement Method of the quasi- fluxoid LDPC code applied to quantum communication system first with European geometry method structure A quasi-cyclic matrix is made, is then based on the mutually orthogonal quasi-cyclic matrix H of the matrix construction twoxAnd Hz；Recycle the two The quasi- fluxoid LDPC code of matrix construction；Finally to HxAnd HzRow dilution processing is done, constructs enhanced quantum LDPC code.
Further, the Enhancement Method of the quasi- fluxoid LDPC code applied to quantum communication system includes following step Suddenly：
(1) arrange parameter m and q obtains the European geometry EG (m, q) on GF (q), is removed in the geometric space by former The straight line of point, the interconnection vector of remaining J straight line can be divided into t cycle class, and it is N that each cycle class, which is a size, Square formation；Line number is constructed as N using this, columns is the matrix H of t*NEG：
HEG=[H0,H1,…,Ht-1]；
Wherein each submatrix HiAll it is the Theory of Circular Matrix that a size is N；
(2) to the H in step (1)EGIt does following processing and obtains matrix H, the number that submatrix is recycled in H is denoted as n, wherein n For even number：
(3) quasi- fluxoid LDPC code is constructed：
3a) enable Hx=[H0,H1,…,Hn-1,Hn], wherein HxFor correcting the phase error of quantum bit；
3b) enableWherein HzFor correcting the bit-errors of quantum bit；
3c) the quasi- fluxoid LDPC code on construction GF (4), check matrix are：
(4) the quasi- fluxoid LDPC code in step (3) is further enhanced：
4a) setting enhancing factor alpha, meets the even-multiple that n is α；
The sparse processing of row 4b) is done to the H in step (2) and obtains the α quasi-cyclic matrixes isometric with H.It is denoted as Mi, 0≤i ＜ α；Wherein MiKth (k meets k% α=i) a submatrix be k-th of submatrix H in Hk, remaining position is and HkIt is equal in magnitude Full null matrix；
4c) construct enhanced quasi- fluxoid LDPC code：
4c1) by step 4b) in obtained α matrix cascade obtain H up and downx：
4c2) to step 4b) in α matrix convert.To arbitrary Mi, keep zero submatrix position constant, for non-zero Submatrix using center as axis, will be exchanged before and after position, then do transposition operation respectively again, obtain M 'i, after this α transformation Matrix cascades obtain H up and downz：
4c3) the enhanced quasi- fluxoid LDPC code on construction GF (4), check matrix are：
(5) belief propagation algorithm is utilized into row decoding to the quantized code obtained in step (3) and step (4).
Further, in the step (1) based on European geometry EG (m, q), but the vertical element number of origin：
Be divided into cycle class number be：
Each the size of cycle class is：
N=qm-1。
Further, the step 3a) and 3b) in obtained HxAnd HzThere is following relationship：
For circular matrix HiAnd HjMeet HiHj=HjHi, so HxAnd HzIt is orthogonal, this is that construction Quantum Error Correcting Codes must The condition that must meet；Wherein Hz TRepresent HzTransposition.
Further, the step 4c1) and 4c2) in construct HxAnd HzAnd it is orthogonal, i.e.,：
HxHz T=0；
Meet the condition of construction quantized code.
In conclusion advantages of the present invention and good effect are：By the Enhancement Method of the present invention, in the fixed feelings of code length Under condition, it can flexibly change code check to increase the number of check bit, so as to obtain better error-correcting performance；It is different by setting Enhancing coefficient to meet to the requirement of error-correcting performance under different application scene, therefore by quasi- internal circulating load subcode be extended to long code should With scene, versatility is improved.
Description of the drawings
Fig. 1 is the Enhancement Method of the quasi- fluxoid LDPC code provided in an embodiment of the present invention applied to quantum communication system Flow chart.
Fig. 2 is the frame error rate of embodiment 1 provided in an embodiment of the present invention and error sign ratio performance simulation figure.
Fig. 3 is the frame error rate of embodiment 2 provided in an embodiment of the present invention and error sign ratio performance simulation figure.
Specific embodiment
In order to make the purpose , technical scheme and advantage of the present invention be clearer, with reference to embodiments, to the present invention It is further elaborated.It should be appreciated that the specific embodiments described herein are merely illustrative of the present invention, it is not used to Limit the present invention.
The mistake control that the enhanced quantized code that the present invention is constructed can be used in the fields such as quantum communications, quantum fault-tolerant calculation System.To realize the reliable communication of high code check and low error rate.
As shown in Figure 1, the increasing of the quasi- fluxoid LDPC code provided in an embodiment of the present invention applied to quantum communication system Strong method includes the following steps：
S101：With one quasi-cyclic matrix of method construct of European geometry, mutually orthogonal based on the matrix construction two Quasi-cyclic matrix HxAnd Hz；
S102：Utilize HxAnd HzConstruct the quasi- fluxoid LDPC code of CSS types；
S103：To HxAnd HzRow dilution processing is done, constructs enhanced quantum LDPC code.
The Enhancement Method of quasi- fluxoid LDPC code provided in an embodiment of the present invention applied to quantum communication system is specific Include the following steps：
(1) arrange parameter m and q obtains the European geometry EG (m, q) on GF (q), is removed in the geometric space by former The straight line of point, the interconnection vector of remaining J straight line can be divided into t cycle class, and it is N that each cycle class, which is a size, Square formation.The present invention constructs line number as N using this, and columns is the matrix H of t*NEG：
HEG=[H0,H1,…,Ht-1]；
Wherein each submatrix HiAll it is a circular matrix；
(2) to the H in step (1)EGIt does following processing and obtains matrix H, the number that submatrix is recycled in H is denoted as n, wherein n For even number：
(3) quasi- fluxoid low-density checksum LDPC code is constructed：
3a) enable Hx=[H0,H1,…,Hn-1,Hn], wherein HxFor correcting the phase error of quantum bit；
3b) enableWherein HzFor correcting the bit-errors of quantum bit；
3c) the quasi- fluxoid low-density checksum LDPC code on construction GF (4), check matrix are：
(4) the quasi- fluxoid low-density checksum LDPC code in step (3) is further enhanced：
4a) setting enhancing factor alpha, meets the even-multiple that n is α；
The sparse processing of row 4b) is done to the H in step (2) and obtains the α quasi-cyclic matrixes isometric with H.It is denoted as Mi, 0≤i ＜ α；Wherein MiKth (k meets k% α=i) a submatrix be k-th of submatrix H in Hk, remaining position is and HkIt is equal in magnitude Full null matrix；
4c) construct enhanced quasi- fluxoid low-density checksum LDPC code：
4c1) by step 4b) in obtained α matrix cascade obtain H up and downx：
4c2) to step 4b) in α matrix convert.To arbitrary Mi, keep zero submatrix position constant, for non-zero Submatrix using center as axis, will be exchanged before and after position, then do transposition operation respectively again, obtain Mi', by this α obtained change Matrix after changing cascades up and down obtains Hz：
4c3) the enhanced quasi- fluxoid LDPC code on construction GF (4), check matrix are：
(5) belief propagation algorithm is utilized into row decoding to the quantized code obtained in step (3) and step (4).
The application principle of the present invention is further described with reference to specific embodiment.
The enhanced quantum low-density parity check LDPC code that the present invention constructs provides following two embodiments：
Embodiment 1, based on European geometry EG (4,2), construction quantum code check is 0.75 quasi-cyclic code, and then it is done and is increased The enhancing of strong factor alpha=2 obtains the enhancing code that quantum code check is 0.5.Realize that step is as follows：
(1) the parameter m=4, q=2 of European geometry is set to obtain the quasi-cyclic matrix H based on European geometry EG (4,2)EG。 The matrix is made of 7 submatrixs, i.e.,：
HEG=[H0,H1,H2,H3,H4,H5,H6]；
Wherein each submatrix HiAll be a size be 15 circular matrix, HiCorresponding generator polynomial is：
gi(x)=xi+1+1；
(2) since the number of the cycle submatrix in step (1) is odd number, so the unit matrix that one size of cascade is 15 As H7, obtain a new quasi-cyclic matrix H；
(3) quasi- fluxoid LDPC code is constructed.
3a) it is configured to correct the matrix H of the phase error of quantum bitx, enable：
Hx=H=[H0,H1,…,H7]；
3b) it is configured to correct the matrix H of the bit-errors of quantum bitz, enable：
3c) the quasi- fluxoid LDPC code on construction GF (4), by 3a) and 3b) in the matrix H that constructsxAnd HzMeet following Relationship：
It can be seen that HxAnd HzIt is orthogonal, it is possible to which, for constructing quantized code, check matrix is：
(4) quantized code in step (3) is further enhanced.
4a) setting enhancing factor alpha=2.
Sparse processing 4b) is made to the H-matrix in step (2), obtaining two matrixes isometric with H is respectively：
M0=[H0,0,H2,0,H4,0,H6,0]；
M1=[0, H1,0,H3,0,H5,0,H7]；
4c) construct enhanced quasi- fluxoid LDPC code：
4c1) using step 4b) in obtained two matrixes cascade up and down as Hx, i.e.,：
4c2) to step 4b) in obtained two matrixes convert.To arbitrary Mi, the position for keeping zero submatrix is constant, Non-zero submatrices will exchange before and after position using center as axis, then do transposition operation respectively, obtain Mi', after the two are converted Matrix up and down cascade obtain Hz, i.e.,：
4c3) the enhanced quasi- fluxoid LDPC code on construction GF (4), to step 4c1) and the 4c2) H of constructionzAnd Hx Have：
It can be seen that HxAnd HzAlso meet orthogonality relation, can be used for constructing a quantized code, check matrix is：
(5) belief propagation algorithm is utilized into row decoding to the quantized code obtained in step (3) and step (4).
Embodiment 2, based on European geometry EG (5,2), construction quantum code check is 7/8 quasi-cyclic code, and then it is distinguished The enhancing of enhancing factor alpha=2 and α=4 is done, obtains the enhancing code that quantum code check is 3/4 and 1/2.Realize that step is as follows：
(1) the parameter m=5, q=2 of European geometry is set to obtain the quasi-cyclic matrix H based on European geometry EG (5,2)EG。 The matrix is made of 15 submatrixs, i.e.,：
HEG=[H0,H1,…,H14]；
Wherein each submatrix HiAll be a size be 31 circular matrix, HiCorresponding generator polynomial is：
gi(x)=xi+1+1；
(2) since the number of the cycle submatrix in step (1) is odd number, so the unit matrix that one size of cascade is 31 As H15, obtain a new quasi-cyclic matrix H；
(3) quasi- fluxoid LDPC code is constructed.
3a) it is configured to correct the matrix H of the phase error of quantum bitx, enable：
Hx=H=[H0,H1,…,H15]；
3b) it is configured to correct the matrix H of the bit-errors of quantum bitz, enable：
3c) the quasi- fluxoid LDPC code on construction GF (4), by 3a) and 3b) in the matrix H that constructszAnd HxMeet following Relationship：
It can be seen that HzAnd HxIt is orthogonal, it is possible to which, for constructing quantized code, check matrix is：
(4) the quantized code work in step (3) is enhanced.
4a) setting enhancing factor alpha=2；
Sparse processing 4b) is made to the H-matrix in step (2), obtaining two matrixes isometric with H is respectively：
M0=[H0,0,H2,0,…,H14,0]；
M1=[0, H1,0,H3,…,0,H15]；
4c) construct enhanced quasi- fluxoid LDPC code：
4c1) using step 4b) in obtained two matrixes cascade up and down as Hx, i.e.,：
4c2) to step 4b) in obtained two matrixes convert, to arbitrary Mi, the position for keeping zero submatrix is constant, Non-zero submatrices will exchange before and after position using center as axis, then do transposition operation respectively, obtain Mi', after the two are converted Matrix up and down cascade obtain Hz, i.e.,：
4c3) the enhanced quasi- fluxoid LDPC code on construction GF (4), to step 4c1) and the 4c2) H of constructionxAnd Hz Have：
It can be seen that HxAnd HzMeet orthogonality relation, can be used for constructing a quantized code, check matrix is：
(5) quantized code in step (3) is continued to do enhances.
5a) setting enhancing factor alpha=4；
Sparse processing 5b) is made to the H-matrix in step (2), obtaining 4 matrixes isometric with H is respectively：
M0=[H0,0,0,0,H4,0,0,0,…,H12,0,0,0]
M1=[0, H1,0,0,0,H5,0,0,…,0,H13,0,0]
M2=[0,0, H2,0,0,0,H6,0,…,0,0,H14,0]
M3=[0,0,0, H3,0,0,0,H7,…,0,0,0,H15]；
5c) construct enhanced quasi- fluxoid LDPC code：
5c1) using step 5b) in obtained four matrixes cascade up and down as Hx, i.e.,：
5c2) to step 5b) in obtained four matrixes convert, to arbitrary Mi, keep the position of zero submatrix not Become, non-zero submatrices will exchange before and after position using center as axis, then do transposition operation respectively, obtain Mi'.By this four changes Matrix after changing cascades up and down obtains Hz, i.e.,：
5c3) the enhanced quasi- fluxoid LDPC code on construction GF (4), to step 5c1) and the 5c2) H of constructionxAnd Hz Have：
It can be seen that HxAnd HzAlso meet orthogonality relation, can be used for constructing a quantized code, check matrix is：
(6) quantized code obtained in step (3), step (4) and step (5) is translated using belief propagation algorithm Code.
The application effect of the present invention is explained in detail with reference to emulation.
1st, simulated conditions：Experiment simulation is based on the quantum low-density parity check LDPC code on GF (4), selects depolarization letter Road and confidence spread BP decoding algorithms do the performance simulation of quantum communication system.
2nd, emulation content：Emulation 1：LDPC is examined to the quasi- fluxoid low-density parity constructed in the embodiment of the present invention 1 The enhanced quantized code that code and enhancing coefficient are 2, by a depolarization channel, is finally carried out using belief propagation algorithm Decoding, and count its error sign ratio and frame error rate.Simulation result is as shown in Figure 2.
The solid line of spider lable represents that code length is 120 in Fig. 2, and quantum code check is 0.75 quasi- fluxoid low-density parity Verify frame error rate of the LDPC code under depolarization channel.
The solid line of diamond indicia represents that enhancing coefficient is 2 in the present invention in Fig. 2, and code length 120, quantum code check is 0.5 Frame error rate of the enhanced quantum low-density parity check LDPC code under depolarization channel.
The dotted line of spider lable represents that code length is 120 in Fig. 2, and quantum code check is 0.75 quasi- fluxoid low-density parity Verify error sign ratio of the LDPC code under depolarization channel.
The dotted line of diamond indicia represents that enhancing coefficient is 2 in the present invention in Fig. 2, and code length 120, quantum code check is 0.5 Error sign ratio of the enhanced quantum low-density parity check LDPC code under depolarization channel.
As seen from Figure 2, fluxoid low-density checksum LDPC code is directed at by the method for the present invention to be increased After strong coefficient is 2 enhancing, frame error rate and error sign ratio have the decline close to an order of magnitude.
Emulation 2：LDPC code and enhancing system are examined to the quasi- fluxoid low-density parity constructed in the embodiment of the present invention 2 Number is respectively 2 and 4 enhanced quantized codes, by a depolarization channel, finally using belief propagation algorithm into row decoding, And count its error sign ratio and frame error rate.Simulation result is as shown in Figure 3.
The solid line of spider lable represents that code length is 496 in Fig. 3, and quantum code check is 7/8 quasi- fluxoid low-density parity Verify frame error rate of the LDPC code under depolarization channel.
The solid line of diamond indicia represents that enhancing coefficient is 2 in the present invention in Fig. 3, and code length 496, quantum code check is 3/4 Frame error rate of the enhanced quantum low-density parity check LDPC code under depolarization channel.
The solid line of Fig. 3 intermediate cams shape label represents that enhancing coefficient is 4 in the present invention, and code length 496, quantum code check is 1/2 Frame error rate of the enhanced quantum low-density parity check LDPC code under depolarization channel.
The dotted line of spider lable represents that code length is 496 in Fig. 3, and quantum code check is 7/8 quasi- fluxoid low-density parity Verify error sign ratio of the LDPC code under depolarization channel.
The dotted line of diamond indicia represents that enhancing coefficient is 2 in the present invention in Fig. 3, and code length 496, quantum code check is 3/4 Error sign ratio of the enhanced quantum low-density parity check LDPC code under depolarization channel.
The dotted line of Fig. 3 intermediate cams shape label represents that enhancing coefficient is 4 in the present invention, and code length 496, quantum code check is 1/2 Error sign ratio of the enhanced quantum low-density parity check LDPC code under depolarization channel
As seen from Figure 3, fluxoid low-density checksum LDPC code is directed at by the method for the present invention to carry out not After enhancing with enhancing coefficient, quantum code check can reduce with the increase of enhancing coefficient, frame error rate and error sign ratio with It the increase of enhancing coefficient and declines.The error-correcting performance of system gets a promotion.
The foregoing is merely illustrative of the preferred embodiments of the present invention, is not intended to limit the invention, all essences in the present invention All any modification, equivalent and improvement made within refreshing and principle etc., should all be included in the protection scope of the present invention.

Claims (5)

  1. A kind of 1. Enhancement Method of quasi- fluxoid LDPC code applied to quantum communication system, which is characterized in that the application It is followed in the Enhancement Method of the quasi- fluxoid LDPC code of quantum communication system first with one standard of method construct of European geometry Ring matrix is then based on the mutually orthogonal quasi-cyclic matrix H of the matrix construction twoxAnd Hz；Recycle the two matrix constructions accurate Fluxoid LDPC code；Finally to HxAnd HzRow dilution processing is done, constructs enhanced quantum LDPC code.
  2. 2. the Enhancement Method applied to the quasi- fluxoid LDPC code of quantum communication system as described in claim 1, feature It is, the Enhancement Method of the quasi- fluxoid LDPC code applied to quantum communication system includes the following steps：
    (1) arrange parameter m and q obtains the European geometry EG (m, q) on GF (q), is removed in the geometric space by origin Straight line, the interconnection vector of remaining J straight line can be divided into t cycle class, and each class that recycles is the side that a size is N Battle array；Line number is constructed as N using this, columns is the matrix H of t*NEG：
    HEG=[H0,H1,...,Ht-1]；
    Wherein each submatrix HiAll it is the Theory of Circular Matrix that a size is N；
    (2) to the H in step (1)EGIt does following processing and obtains matrix H, the number that submatrix is recycled in H is denoted as n, and wherein n is even Number：
    (3) quasi- fluxoid LDPC code is constructed：
    3a) enable Hx=[H0,H1,...,Hn-1,Hn], wherein HxFor correcting the phase error of quantum bit；
    3b) enableWherein HzFor correcting the bit-errors of quantum bit；
    3c) the quasi- fluxoid LDPC code on construction GF (4), check matrix are：
    (4) the quasi- fluxoid LDPC code in step (3) is further enhanced：
    4a) setting enhancing factor alpha, meets the even-multiple that n is α；
    The sparse processing of row 4b) is done to the H in step (2) and obtains the α quasi-cyclic matrixes isometric with H.It is denoted as Mi, 0≤i ＜ α；Its Middle MiKth (k meets k% α=i) a submatrix be k-th of submatrix H in Hk, remaining position is and HkIt is equal-sized complete Null matrix；
    4c) construct enhanced quasi- fluxoid LDPC code：
    4c1) by step 4b) in obtained α matrix cascade obtain H up and downx：
    4c2) to step 4b) in α matrix convert.To arbitrary Mi, keep zero submatrix position constant, for the sub- square of non-zero Battle array, using center as axis, will exchange before and after position, then does transposition operation respectively again, obtain Mi', by the matrix after this α transformation Cascade obtains H up and downz：
    4c3) the enhanced quasi- fluxoid LDPC code on construction GF (4), check matrix are：
    (5) belief propagation algorithm is utilized into row decoding to the quantized code obtained in step (3) and step (4).
  3. 3. the Enhancement Method applied to the quasi- fluxoid LDPC code of quantum communication system as claimed in claim 2, feature It is, based on European geometry EG (m, q) in the step (1), but the vertical element number of origin：
    Be divided into cycle class number be：
    Each the size of cycle class is：
    N=qm-1。
  4. 4. the Enhancement Method applied to the quasi- fluxoid LDPC code of quantum communication system as claimed in claim 2, feature Be, the step 3a) and 3b) in obtained HxAnd HzThere is following relationship：
    For circular matrix HiAnd HjMeet HiHj=HjHi；So HxAnd HzIt is orthogonal, this is that construction Quantum Error Correcting Codes must expire The condition of foot；Wherein Hz TRepresent HzTransposition.
  5. 5. the Enhancement Method applied to the quasi- fluxoid LDPC code of quantum communication system as described in claim 1, feature Be, the step 4c1) and 4c2) in construct HxAnd HzAnd it is orthogonal, i.e.,：
    HxHz T=0
    Meet the condition of construction quantized code.
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